6.1. How the Installer Works

The Debian Installer consists of a number of special-purpose
components to perform each installation task. Each component performs
its task, asking the user questions as necessary to do its job.
The questions themselves are given priorities, and the priority
of questions to be asked is set when the installer is started.

When a default installation is performed, only essential (high priority)
questions will be asked. This results in a highly automated installation
process with little user interaction. Components are automatically run
in sequence; which components are run depends mainly on the installation
method you use and on your hardware. The installer will use default values
for questions that are not asked.

If there is a problem, the user will see an error screen, and the
installer menu may be shown in order to select some alternative
action. If there are no problems, the user will never see the
installer menu, but will simply answer questions for each component
in turn. Serious error notifications are set to priority
“critical” so the user will always be notified.

Some of the defaults that the installer uses can be influenced by passing
boot arguments when debian-installer is started. If, for example, you wish to
force static network configuration (DHCP is used by default if available),
you could add the boot parameter netcfg/disable_dhcp=true.
See Section 5.2.1, “Debian Installer Parameters” for available options.

Power users may be more comfortable with a menu-driven interface,
where each step is controlled by the user rather than the installer
performing each step automatically in sequence. To use the installer
in a manual, menu-driven way, add the boot argument
debconf/priority=medium.

If your hardware requires you to pass options to kernel modules as
they are installed, you will need to start the installer in
“expert” mode. This can be done by either using the
expert command to start the installer or by adding
the boot argument debconf/priority=low.
Expert mode gives you full control over debian-installer.

The normal installer display is character-based (as opposed to the now
more familiar graphical interface). The mouse is not operational in
this environment. Here are the keys you can use to navigate within the
various dialogs. The Tab or right
arrow keys move “forward”, and the Shift-Tab or left arrow keys
move “backward” between displayed buttons and selections.
The up and down arrow select
different items within a scrollable list, and also scroll the list
itself. In addition, in long lists, you can type a letter to cause the
list to scroll directly to the section with items starting with the
letter you typed and use Pg-Up and
Pg-Down to scroll the list in sections. The
space bar selects an item such as a checkbox. Use
Enter to activate choices.

Error messages are redirected to the third console.
You can access this console by
pressing Left Alt-F3
(hold the left Alt key while pressing the
F3 function key); get back to
the main installer process with
Left Alt-F1.

These messages can also be found in
/var/log/messages. After installation, this log
is copied to /var/log/debian-installer/messages on your
new system. Other installation messages may be found in
/var/log/ during the
installation, and /var/log/debian-installer/
after the computer has been booted into the installed system.